Re: [Xen-devel] [PATCHv2 3/6] xen: generic xadd() for ticket locks

[Tim Deegan <tim@xxxxxxx>]

At 15:19 +0100 on 10 Apr (1428679194), David Vrabel wrote:
> Provide a generic xadd() implementation for architectures that don't
> provide one.
> 
> This is only temporary until arm/arm64 provides an xadd()
> implementation.
> 
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>

The logic looks fine, but please:
 - add a comment explaining what it does; and
 - convert it to Xen coding style to match the rest of the file. 

With that,

Reviewed-by: Tim Deegan <tim@xxxxxxx>

Cheers,

Tim.

> ---
>  xen/common/spinlock.c |   21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/xen/common/spinlock.c b/xen/common/spinlock.c
> index 5fd8b1c..0c4289c 100644
> --- a/xen/common/spinlock.c
> +++ b/xen/common/spinlock.c
> @@ -10,6 +10,27 @@
>  #include <asm/processor.h>
>  #include <asm/atomic.h>
>  
> +#ifndef xadd
> +
> +static u32 generic_xaddl(volatile u32 *ptr, u32 v)
> +{
> +    u32 old, new, prev;
> +
> +    old = read_atomic(ptr);
> +    for(;;) {
> +        new = old + v;
> +        prev = cmpxchg(ptr, old, new);
> +        if (prev == old)
> +            break;
> +        old = prev;
> +    }
> +    return old;
> +}
> +
> +#define xadd(ptr, v) generic_xaddl((ptr), (v))
> +
> +#endif
> +
>  #ifndef NDEBUG
>  
>  static atomic_t spin_debug __read_mostly = ATOMIC_INIT(0);
> -- 
> 1.7.10.4
> 
> 
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